Hydrographic changes in the waters between Iceland and Jan Mayen in the last decade

Abstract

During the last few years a change has taken place in the proportions of the different water masses in the East-Icelandic Current northeast of Iceland (Fig. 1).It is shown that the current has changed from being an ice-free arctic current in 1948-1958 to a polar current in 1964-1968, transporting drift ice and preserving it, especi.ally in the years 1965, 1967 and 1968.As seen in Fig. 2 the salinity of 34.7%c is of special interest in the area these last years.As demonstrated in Fig. 11 this salinity is the critical one for the area in question, should the surface layer cool doiun to freezing point, -1.8° C. At salinities of 34.7%c or lower the surface water will not reach a density high enough to start a deep vertical convection even at a temperature of -1.8° C, but at salinities of 34,8%c or more this is possible.That means in the latter case a deep vertical convection before such a strong cooling is reached.The drift ice conditions were extremely unfavourable in North ancl East Icelandic waters in the spring of 1965, 1967 and 1968.Thus a close relationship between drift ice and hydrographic conditions in the Easl-Icelandic Current is establishecl, throwing light on the physical causes of the situation.A knoiuledge of the stratification, i. e. the salinity in the surface layer, in late xuinter betiueen Iceland and Jan Mayen, may, in connection xuith knowledge of the atmospheric circulation and air temperature, be a tool for the precliction of ice in Icelandic luaters in spring and summer.!